In the field of photomechanical process technology, photographic materials with excellent original-producibility, stable processing solutions and simplified replenishment systems are required for the purpose of dealing with today's diversified and complicated print forms.
Originals to be employed in a line work process are often composed of phototypeset-letters, hand-written letters, illustrations and halftone dot image photographs. Accordingly, the original contains plural images having different concentrations and different line widths in combination. Photomechanical cameras and photographic materials suitable for finishing the images from such originals with good reproducibility as well as image-forming methods applicable to such photographic materials are earnestly desired in this technical field.
For the photomechanical process of producing catalogs or large-sized posters, enlargement or reduction of dot image photographs is widely used. In the photomechanical process using enlarged dot images, the dots become coarsened to give blurred photoprints. On the other hand, in the photomechanical process of forming reduced photoprints, fine dots with an enlarged ratio of lines/inch are to be photographed. Accordingly, an image-forming method with a much broader latitude assuring the formation of fine black dots in the white background and fine white dots in the black background is desired for the purpose of maintaining the reproducibility of halftone dot images in the photomechanical process.
As the light source for a photomechanical camera, a halogen lamp or xenon lamp is employed. In order to obtain a sufficient photographing sensitivity to the light source, the photographic material to be employed in the photomechanical process is generally ortho-sensitized. However, it was found that the ortho-sensitized photographic materials are much more influenced by chromatic aberrations of the lens, and therefore the quality of the images to be formed are frequently worsened by such influence. It was further found that the deterioration of image quality is more noticeable where a xenon lamp is used as the light source.
As a system of satisfying the demand for an image-forming method with a broad latitude, a method is known where a lith-type silver halide photographic material composed of silver chlorobromide (having a silver chloride content of at least 50 mol % or more) is processed with a hydroquinone-containing developer where the effective concentration of the sulfite ion therein is extremely lowered (generally, to 0.1 mol/liter or less) to thereby obtain a line image or halftone dot image having a high contrast and a high blackened density where the image portions and the non-image portions are clearly differentiated from each other. However, the method has various drawbacks. Specifically, since the sulfite concentration in the developer to be employed in the method is low, development is extremely unstable due to aerial oxidation. For the purpose of stabilizing the activity of the processing solution, various means have been employed. In addition, processing speed is extremely slow, and the working efficiency is poor under the current situation.
Accordingly, an improved image-forming system is desired, which is free from the instability of the image formation in the above-mentioned development method (lith-development system) and which may be processed with a processing solution having excellent storage stability to provide photographic images having ultra-hard photographic characteristics. As one example, a system of forming an ultra-hard negative image having a gamma value of more than 10 has been proposed, for example, in U.S. Pat. Nos. 4,166,742, 4,168,977, 4,221,857, 4,224,401, 4,243,739, 4,272,606 and 4,311,781, where a surface latent image-type silver halide photographic material containing a particular acyl hydrazine compound is processed with a developer having an excellent storage stability which contains a sulfite preservative in an amount of 0.15 mol/liter or more and has a pH value of from 11.0 to 12.3. The above proposed image-forming system is characterized in that a silver iodobromide or silver chloroiodobromide-containing photographic material can be processed, whereas only a silver chlorobromide photographic material having a high silver chloride content can be processed by the conventional ultra-hard image-forming method.
The above proposed image-forming system is excellent in the point that an image with sharp halftone dot image quality is formed, the process proceeds stably at a high speed, and the reproducibility of the original used is good. However, a further improved system with a further elevated original reproducibility is still desired for the purpose of satisfactorily dealing with today's diversified print forms.
Photographic materials containing a redox compound capable of releasing a photographically useful group by oxidation are mentioned in JP-A-56-153336, 61-156043, 61-230135 and 62-296138, where increased gradation reproducing latitude is intended. (The term "JP-A" used herein means an unexamined published Japanese patent application.) However, it has been found that redox compounds incorporated into these proposed photographic materials are inconvenient because they interfere with the hard contrast of images formed where the materials are processed in an ultra-hard processing system. Therefore, the compounds could not display the characteristics of an ultra-hard processing system.